You use Ultimate Diesel in a ZT?!?
Unlike super unleaded it's a waste of money buying premium diesel imho.
I have 120k of data that suggests branded/premium diesel gives slightly better mpg, possibly burning more cleanly. Shell for example use a gas to liquid process for it’s premium diesel unlike anyone else im aware of.
My best average result is with normal Shell diesel at 37mpg (stop laughing, it’s an inefficient old 4x4 with 120k on it), the worst is Harvester at 31mpg, all the supermarket stuff averages out within 1mpg of each other (32-33mpg), the best value is Costco Premium which returns an average of 34mpg but is cheaper than supermarket fuel. Now all of that is within a relatively consistent range of deviation allowing for driving conditions, temperature, winter fuel additive and sample size etc. and objectively is only suggestive at best.
What I can’t dismiss as easily is the variable vane system on my turbo, after 120k of service the control ring has become slightly sticky, it’s only noticeable under hard acceleration up hill when down shifting, but it’s repeatable, daily. If I run supermarket/no name fuel it happened daily at the same place, if i run Shell/BP/Costco premium fuel, then I don’t have the problem. The same behaviour has been reported by other owners with the same engine/issue.
Have I bored everyone to death yet?